It takes a great deal of work to produce a tiny amount of essential oil. Sixty thousand Rose blossoms are required to produce just one ounce of Rose oil, whereas in the Lavender plant the essential oil is more abundant and 220 pounds will provide seven pounds of oil. In the case of Jasmine, the flowers must be picked by hand before the sun becomes hot on the very first day they open, whereas the Sandalwood tree must be thirty years old and thirty feet high before it is cut down for distillation. The price of each oil reflects these conditions and because it takes eight million hand-picked jasmine blossoms to produce 2.2. pounds of oil, you can understand why that is one of the most expensive oils on the market.
On average, an essential oil contains one hundred components, many of which have yet to be discovered. Each one works harmoniously and synergistically with the other to encourage various therapeutic effects which is why the standards for quality and purity are the highest for aromatherapeutic use. Understanding just a little of what goes into the extraction of an oil clarifies why better quality oils are more expensive.
Unscrupulous suppliers will often dilute a pure essential oil with a carrier base without informing the end-consumer or perhaps use different less costly oils in combination to "recreate" a more expensive oil. For example, Carnation oil is very expensive. Black Pepper and Ylang-Ylang oils are combined to create the aroma of Carnation. This is all very well if perfumery is your concern, but no good at all if the Carnation oil is required for a therapeutic purpose. And often times, these suppliers will remove one component and substitute a chemical, lowering their cost.
So what can the average consumer do? Front labels are often deceiving, so don’t rely on the name of the product. Be sure to shop with a company that is concerned about health, not perfumes. Look at the ingredient listing on each bottle. Be sure it is the oil you are looking for and states that it is a "pure, essential oil" and preferably organic. The best judge of quality is undoubtedly the human nose (perfumers must study for years before their olfactory senses are developed enough to do a professional job), it is often the case that a synthetic aroma will smell more pungently of the raw material that the real thing. Do not be influenced by strength, but rather by price, supplier reputation and, in time, your own experience and instinct.
The best companies to buy through are proud of the purity of their oils and will often make available to it’s consumers the method of extraction and the location of the plants growth. Please do keep in mind, pure essential oils are potent and have strong medicinal uses. When applying to skin, most oils need to be blended with a carrier oil (jojoba/olive/argan etc) although when using a diffuser, it can be used full strength.